COMPAEATIVE HISTOLOGY AND PHYSIOLOGY OF THE SPLEEN. 277 



In the spleen of the Frog the reticulum of the pulp consists of large branching cells, 

 the plate-like processes of which do not taper so much before joining with others as in 

 the spleen of the fish. The processes are so much expanded that sometimes the sec- 

 tional area seems to be chiefly occupied by them, the meshes appearing as comparatively 

 small fenestra? in a nucleated membrane. When the processes are seen in oblique 

 section or in profile, they appear like narrow bands in the one case or somewhat fine 

 threads in the other. (Plate II. fig. 8.) Each cell contains usually one large, oval, 

 slightly granular, faintly blue-stained nucleus, but there are sometimes two, three or 

 four. The meshes of the reticulum vary much in size and shape. The processes of the 

 cells of the reticulum appear to be continuous with the walls of the venous sinuses, and 

 to join the outer wall of the artery. 



The cells of the pulp are mainly of five kinds in addition to the red blood-corpuscles : 

 — (1) Round lymphoid cells resembling free nuclei are far the most abundant. They vary 

 in size from a half to four or five times the size of the nucleus of a red blood-corpuscle. 

 (2) Round protoplasmic corpuscles apparently identical with the small leucocytes. Their 

 size is a little more than half that of the red blood-corpuscles, and they are composed 

 of finely granular protoplasm, staining faintly pink with eosine, in which is imbedded 

 sometimes a single small round nucleus that stains somewhat deeply blue with hsema- 

 toxylin ; but more usually there are two or three such in a single cell. (3) Large proto- 

 plasmic corpuscles about twice the size of a red blood-corpuscle, which seem to be iden- 

 tical with the large leucocytes. They are best seen in the intracapsular venous sinuses, 

 but are far more numerous in the parenchyma immediately underneath the capsule. 

 They consist of somewhat finely granular protoplasm, that stains faintly blue with hsema- 

 toxylin, and from three to eight faintly stained nuclei. They sometimes show very 

 large karyokinetic figures. (4) Round or oval cells, found especially near the middle 

 of the pulp, about the size of the small leucocyte, whose protoplasm is in the form of 

 round coarse granules, which stain very deeply pink with eosine, each having a single, 

 oval, blue-stained nucleus. These probably correspond with the eosinophilous cells of 

 Waldeyer. (5) Cells containing pigment are especially numerous in the outer zone of 

 the parenchyma and particularly in the winter frog. In shape they are round or oval, 

 and are similar in size to the large leucocytes. They have a single nucleus usually, but 

 sometimes they are multinucleated. The smaller consist of granular, faintly blue-stained 

 protoplasm, in which are scattered numerous dark brown granules. The larger appear 

 to consist almost entirely of pigment particles, the nucleus being pushed to the peri- 

 phery of the cell. The cells appear sometimes to be vacuolated. In very thin sections, 

 some of the larger pigment masses are seen to be composed of oval parcels of pigment 

 granules, each parcel being about the size of a red blood-corpuscle, and containing a 

 faintly blue-stained nucleus near its margin. This appearance suggests that each oval 

 parcel may be a degenerated red blood-corpuscle. The pigment does not blacken with 

 ammonium sulphide. 



Within the intracapsular venous sinuses of the winter frog, and in the summer frog, 



VOL. XXXVIII. PART II. (NO. 8). 2 T 



